1. Field of the Invention
This invention relates to screen hangers for use in supporting a gravel pack screen in a well bore, and more particularly, to a screen hanger adapted to compensate for thermal expansion as a result of heat such as is present in steam flood or steam injection wells.
2. Description of the Prior Art
Packers used for supporting liner screens adjacent a gravel packed well formation are known in the art. These packers often serve to act as hangers to support the screen as well as seal the well annulus above the screen. Typically, such packers are rigidly attached to the screen and utilize elastomeric seal elements, such as rubber.
Most previous packers known in the art are not suitable in high temperature situations such as occur in steam flood or steam injection wells. Once such packers are set, there is no provision made for compensating for the extreme changes in temperatures and the resultant thermal expansion of the components. The apparatus of the present invention solves this problem by utilizing a totally floating mandrel inside a packer portion. Once the packer has been set, and heat is applied in the well, the mandrel, which is the only portion of the apparatus connected to the liner screen, is free to expand or contract as conditions dictate.
One prior apparatus which provides thermal compensation is manufactured by Chancellor Oil Tools in Bakersville, Caif. This apparatus has a mandrel which may expand in a longitudinal direction and which is guided in part by slip supports sealed by O-rings thereon. The Chancellor apparatus has slips below the packer element unlike the present invention which utilizes slips above and below the packer to rigidly locate and restrain the packer in a set position.
Another problem with previous gravel packing apparatus in high temperature situations is that the elastomeric sealing members are not adequate. It is well known that elastomeric elements, such as rubber, harden and sometimes shrink when subjected to high temperatures. Thus, these materials are not suitable for sealing when high temperatures are present.
The apparatus of the present invention preferably utilizes a thermal seal element of a heat resistant material. Such materials include, but are not limited to, lead and thermoplastics. Lead is particularly good because it is inexpensive. The Chancellor apparatus also uses a lead seal, but because the seal is not restrained by upper and lower slips, it is possible that the seal could be undesirably extruded when pressure is applied thereto.
The apparatus of the present invention is designed to be made relatively inexpensively compared to most packers. The use of collet-type slips reduces the number of parts, as compared to previous packers.
One old method of packing a liner screen in a well having high temperatures consists of driving a lead seal into the well annulus around the liner to seal the annulus at the top of the liner after completion of the gravel packing operation. This system is unsatisfactory in that compensation for thermal expansion of the liner is not provided and requires an additional trip out of the well, unlike the present invention which needs just one trip. Further, the lead seal of the previous method is not as securely set and located as with the present invention.